1. Field of the Invention
The present invention relates to an auger type ice making machine for scratching off an ice layer grown on the inner surface of a refrigeration casing which is cooled from the outside by a helical blade of an auger, compressing the scratched ice and discharging the same as ice particles.
2. Description of the Related Art
In an auger type ice making machine, although the upper rotary shaft of an auger rotating about a vertical axis is supported in a radial direction by a press head, a large force resulting from a reaction force produced when an ice layer is scratched off is applied to the auger in a downward direction. Further, since ice is pushed out through an ice compression passage passing though the press head, an upward force acts on the press head. Therefore, since there is a tendency that a gap between the upper shoulder surface of the auger and the lower end surface of the press head is increased, impurities are liable to enter the bearing portion of the upper rotary shaft. Further, impurities such as silica and the like in ice making water in the refrigeration casing tends to concentrate at the upper portion of the refrigeration casing on which the press head is disposed to compress and dehydrate sherbet like ice, by which the concentration of impurities is increased in the vicinity of the upper shoulder surface of the auger.
Therefore, the bearing unit of the upper rotary shaft of the auger which is supported by being inserted into the press head has many problems to be solved, to which many proposals have been made.
For example, according to the proposal of Japanese Patent Laid-Open No. 58-21020, a downward force applied to an auger is transmitted to a press head through a specially provided thrust bearing so that an upward force applied to the press head is canceled by the downward force. At the same time, a radial direction load applied to the auger is supported by a ball bearing and the auger is isolated from an ice making space by an oil seal with a lip. Although a problem caused by a thrust load is solved by the proposal, however, there remains a problem that the lip is liable to be damaged because sherbet like ice and foreign substances such as silica and the like are pressed against the oil seal, the ball bearing is damaged by the invasion of water and foreign substances and lubricant leaks.
According to the proposal of Japanese Utility Model Laid-Open No. 60-187887, a seal composed of a groove having a plurality of steps is formed to a gap between a space containing ice making water and a bearing unit to prevent the invasion of foreign substances such as silica and the like and sherbet like ice into the bearing unit. Since the seal refrigerates ice previously invades into the groove to thereby prevent the invasion of the foreign substances such as silica and the like, it is effective when operation is carried out for a considerable period of time. However, the effect for preventing the invasion of the foreign substances cannot be expected just after the start of operation.
According to the proposals of Japanese Utility Model Publications Nos. 61-32304 and 3-36858, although abnormal wear of a press head and the upper shoulder surface of an auger is prevented by an independent hard washer interposed between the press head and the upper shoulder surface of the auger, since a force acts as described above, a gap therebetween tends to increase and this arrangement does not much contribute to prevent the invasion of foreign substances to a bearing unit.
As described above, although there are proposals for independently cope with various problems of the bearing unit of the upper rotary shaft of an auger, none of them does not satisfactorily solve the problems as a whole.
Taking the above fact into consideration, the inventors of the present application have proposed a practically applicable structure using a slide bearing for low speed and high load, the structure being arranged such that a metal layer composed of high-hardness/high corrosion resistance metal is formed on the periphery of the upper rotary shaft of an auger. To explain this structure with reference to FIG. 5, an auger 2 in a refrigeration cylinder includes a helical blade 2a and an upper rotary shaft 2b is supported by a press head 3 through a high load resistant slide bearing 4. A high-hardness metal layer 2c of about 0.5 mm thick is formed to the periphery of the upper rotary shaft 2b. With this arrangement, the damage of the sliding surface of the bearing can be prevented by the combination of the slide bearing 4 and the high-hardness metal layer 2c even if impurities, foreign substances, water and the like invades into a bearing unit. Thus, its life is prolonged about five times longer than a usual one.
As described above, when the high-hardness metal layer is formed on the periphery of the upper rotary shaft of the auger, wear resistant characteristics are greatly improved. When the high-hardness metal layer is formed by thermal splaying, however, pinholes are sometimes formed and there is a possibility that unacceptable portions may be caused by the pinholes. The pinholes are liable to be made on the boundaries between a base metal and the metal layer. In practice, the occurrence of pinholes is prevented in such a manner that the ends of the metal layer is formed to an edge having acute angle on the boundaries between the ends of the metal layer and the base metal.
Consequently, cracks are liable to be produced to the metal layer when the metal layer is cut or ground so that it is subjected to finish machining. More specifically, in the conventional arrangement whose life is prolonged by forming the aforesaid high-hardness metal layer on the periphery of the upper rotary shaft of an auger, there is a problem that pinholes and cracks are liable to be produced at the end of the metal layer in the axial direction thereof in a manufacturing process and rust is produced from them.